The present invention relates to a synchronous motor.
These days, office automation equipments, for example, have DC or AC fan motors for cooling. Especially, in the case of high rotational speed, AC fan motors having two or four magnetic poles are preferably employed.
The inventor invented synchronous motors (see JP7-232268, JP8106929, etc.), each of which has armature coils and a rectifying circuit, which includes a diode, a brush, a commutator, etc. and is connected to the coils; and each of the motors rectifies AC current, which is supplied from an AC power source, and starts to rotate a permanent magnet rotor, as a DC motor, until its rotational speed reaches near synchronous speed, then the commutator is mechanically disconnected from the rectifying circuit so as to transfer to synchronous operation with the AC power source.
A two-magnetic pole synchronous motor has rotational speed of 3,000 rpm (50 Hz) or 3,600 rpm (60 Hz), small size, high working efficiency and applicability, so it is preferably used as an AC fan motor, etc.
An example of an outer rotor-type two-magnetic pole synchronous motor is shown in FIGS. 17 and 18. A commutator 101 is capable of moving in an axial direction of an output shaft 102 so as to mechanically changing operational state from a start operation to a synchronous operation. A ring-shaped permanent magnet rotor (not shown), in which two magnetic poles are provided with angular separation of 180xc2x0, is coaxial to the commutator 101 and attached to the output shaft 102. The permanent magnet rotor is started by magnetic repulsion, which is occurred when electric current flows through armature coils 103. An electric conductive slide ring 104, whose central angle is less than 180xc2x0, is provided to an outer circumferential face of the commutator 101.
When the rotational speed of the permanent magnet rotor reaches near synchronous speed, the commutator 102 is moved in the axial direction, by centrifugal force of a weight not shown, against elastic force of a coil spring (not shown). With this action, a switch 107 electrically disconnects a rectifying circuit 106 from a single-phase AC power source 105 and electrically connects the coils 103 to the power source 105.
The coils 3 are two coil segments: an A-coil and a B-coil. The A-coil and the B-coil are formed by winding a wire round a bobbin, not shown, in a prescribed direction with prescribed turns. Power supply brushes 108a and 108b contact the slide ring 104, which is provided on the outer circumferential face of the commutator 101, so as to alternately supply electric power, so their phases are mutually shifted 180xc2x0. A-power receiving brushes 109a and 109b are used to supply the electric power to the A-coil; B-power receiving brushes 110a and 110b are used to supply the electric power to the B-coil. At least one of the A- and the B-power receiving brushes 109a, 109b, 110a and 110b contacts the slide ring 104 so as to receive the electric power, so phases of the pairs are mutually shifted 180xc2x0. Diodes 111a and 111b are connected to the A-power receiving brushes 109a and 109b and diodes 112a and 112b are connected to the B-power receiving brushes 110a and 110b so as to half-wave-rectify the AC current from the AC power source 105 and supply the half-wave-rectified current to the A-coil and the B-coil (see FIG. 17).
The power supply brushes 108a, 108b, the A-power receiving brushes 109a and 109b and the B-power receiving brushes 110a and 110b are respectively biased radially inward by electrically conductive plate springs 114a, 114b, 115a, 115b, 116a and 116b, which are provided to a housing 113 (see FIG. 18), so that they can contact the slide ring 104 (see FIG. 17).
The AC current supplied from the single-phase AC power source 105 is rectified by the rectifying circuit 106, which is connected to the coils 103, so that the permanent magnet rotor is magnetically started, as the DC motor, until its rotational speed reaches near the synchronous speed. Upon reaching near the synchronous speed, the commutator 101 is mechanically disconnected from the rectifying circuit 106, and the switch 107 is turned so as to short the AC power source 105 and the coils 103 so as to synchronously rotate the permanent magnet rotor 103. Note that, symbols C1, C2 and C3 stand for capacitors for absorbing surge current.
In the synchronous motors disclosed in JP7-232268, JP8-106929, etc., the permanent magnet rotor is started, as the DC motor, until its rotational speed reaches near the synchronous speed, then the commutator 101 is mechanically moved in the axial direction so as to electrically disconnect from the rectifying circuit 106 and turn the switch 107, so that power consumption can be highly improved in comparison with conventional induction motors, but number of parts must be increased, the structure must be complex and size of the motor cannot be smaller.
The rotor should be transferred from the start operation to the synchronous operation by one action, but the commutator is not always moved smoothly and power swing is sometimes occurred by overload, so that the rotor must be restarted and retransferred, namely the transition of the operation cannot be securely executed.
Further, a plurality of brushes and the slide ring repeatedly contact, so they are abraded and cannot fully contact, especially, in the case of high power motors whose power is 50 W or more, the current is apt to spark when the current direction is changed during the start operation, so safety and reliable synchronous motors are required.
An object of the present invention is to solve the above described problems of the conventional synchronous motors and to provide a small-sized reliable synchronous motor, whose energy consumption is low and which can securely transfer from the start operation to the synchronous operation.
To achieve the object, the present invention has following structures.
Namely, the synchronous motor of a first structure comprises: a permanent magnet rotor being rotatably attached in a housing proper and rotating about an output shaft; and a stator including coils, which are wound round a stator core, characterized by: the coils including an A-coil segment and a B-coil segment, which are connected in series; first measuring means for measuring rotational speed of the permanent magnet rotor and positions of magnetic poles thereof; second measuring means for measuring frequency of an AC power source; a start operation circuit rectifying alternate current, which is supplied from the AC power source, with a rectifying bridge circuit and changing the direction of the rectified current, which flows through the A-coil of the coils, according to rotational angle of the permanent magnet rotor by controlling switching means so as to start the permanent magnet rotor as a DC brushless motor; a synchronous operation circuit shorting the AC power source and the A- and the B-coils so as to synchronously rotate the permanent magnet rotor as an AC synchronous motor; switches being provided between the AC power source and the coils and switching the connection to the synchronous operation circuit; and control means turning off the switches to disconnect the synchronous operation circuit and controlling the switching means during the start operation, starting with suppressing input of inverted minus side of the AC power source, which is full-wave-rectified and flows through the A-coil of the coils via the rectifying bridge circuit, so as to make the current application range of the minus side shorter than that of the plus side, turning off the switching means and turning on the switches when the rotational speed of the permanent magnet rotor, which is measured by the first measuring means, reaches near synchronous speed with respect to the frequency of the power source, which is measured by the second measuring means, thereby the start operation circuit using the A-coil is disconnected and the synchronous operation circuit using the A- and B-coils is connected to transfer to the synchronous operation.
In the synchronous motor, the control means controls the switching means for predetermine time, during the start operation, so as to control the current application range of the inverted minus side of the rectified current, which is supplied from the AC power source and full-wave-rectified, flowing through the A-coil.
The synchronous motor may further comprise: third measuring means including: a sensor plate having slits, which are formed in a circumferential direction so as to introduce the current toward the coils; and an optical sensor detecting the slits, wherein the control means controls the switching means and switching-controls the current direction toward the A-coil of the coils, during the start operation, on the basis of output signals of the optical sensor.
In the synchronous motor, the third measuring means may include: a sensor plate having slits, which are formed in the circumferential direction so as to make the current application range of the inverted minus side of the rectified current, which is supplied from the AC power source and full-wave-rectified, flowing through the A-coil shorter; and an optical sensor for detecting the slits, and wherein the control means controls the switching means so as not to apply the current to the inverted minus side of the rectified current, within a prescribed angular range, on the basis of the output signals of the optical sensor.
In the synchronous motor, the first measuring means may include: a sensor plate having slits and shading sections, which are alternately formed and divide a portion between magnetic poles into odd number of parts; and an optical sensor detecting the slits and the shading sections, wherein the control means controls the switching means, detects the stop pole of the permanent magnet rotor on the basis of the output signals of the optical sensor, supplies the current to the A-coil to securely rotate the permanent magnet rotor in the normal direction during the start operation, switches the current direction toward the A-coil with measuring the rotational angle and the positions of the magnetic poles of the permanent magnet rotor, and apply no current to the inverted minus side of the rectified current within a prescribed angular range.
In the synchronous motor, the control means may repeatedly controls the switches SW1 and SW2 so as to transfer from the synchronous operation to the start operation and transfer to the synchronous operation again when power swing occurs.
In the synchronous motor, the stator core may include main core sections, from each of which a subcore section is extended in the opposite direction of the rotational direction of the permanent magnet rotor, and magnetic permeability of the main core section is greater than that of the subcore section.
In the synchronous motor, the stator may have a bobbin, which is attached to the stator core and includes a core shaft, whose axial line is perpendicular to an axial line of the permanent magnet rotor, and flanges, which are respectively provided to the both ends of the core shaft, and the A-coil and the B-coil are serially wound around the bobbin.
The synchronous motor of a second structure comprises: a permanent magnet rotor being rotatably attached in a housing proper and rotating about an output shaft; first measuring means for measuring rotational speed of the permanent magnet rotor and positions of magnetic poles thereof; second measuring means for measuring frequency of an AC power source; a stator including coils, which are an A-coil and a B-coil wound round a stator core and serially connected via an intermediate tap; a start operation circuit being connected to the AC power source and the intermediate tap of the coils and further connected to the A- and B-coils in parallel with respect to the AC power source, wherein a first and a second diodes for flowing the rectified current through the A-coil and a first and a second transistors, which can be switching-controlled so as to alternately changing the direction of the rectified current, are respectively connected in parallel, a third and a fourth diodes for flowing the rectified current through the B-coil and a third and a fourth transistors, which can be switching-controlled so as to alternately changing the direction of the rectified current, are respectively connected in parallel, the AC current of the AC power source is rectified by a first to a fourth diodes, and the first to the fourth transistors are switching-controlled so as to alternately flow the rectified current through the A-coil and the B-coil according to the rotational angle of the permanent magnet rotor 5 and start the permanent magnet rotor as a DC brushless motor; a synchronous operation circuit being connected to the AC power source and the B-coil so as to synchronously rotate the permanent magnet rotor as an AC synchronous motor; a switch switching the connection between the start operation circuit, to which the AC power sources and the intermediate tap are connected, and the synchronous operation circuit, to which the AC power source and the B-coil are connected; and control means alternately changing the current direction of the rectified current flowing through the coils, turning on/off the third and the fourth transistors of the start operation circuit so as to make a current application angular range, in which the current flows to the coils during one turn of the permanent magnet rotor, of the A-coil greater than that of the B-coil and converge the rectified current to the A-coil during the start operation, turning off the third and fourth transistors, which are connected to the B-coil and turning on the first and second transistors, which are connected to the A-coil when the rotational speed of the permanent magnet rotor, which is measured by the first measuring means, reaches near synchronous speed with respect to the frequency of the power source, which is measured by the second measuring means, and controlling the switch to change the connection from the intermediate tap to the B-coil so as to transfer the synchronous operation by the synchronous operation circuit.
In the synchronous motor, one combination of the third and fourth diodes and the third and fourth transistors, which are respectively connected in parallel, of the start operation circuit may be omitted so as to make current intensity of the A-coil greater than that of the B-coil during the start operation.
In the synchronous motor, the first measuring means may include a sensor plate having slits, which define directions and application range of the current flowing through the A-coil and the B-coil, wherein the first measuring means detects the slits, the control means switching-controls the first to the fourth transistors of the start operation circuit so as to make current intensity of the A-coil greater than that of the B-coil, during the start operation, on the basis of output signals of the first measuring means.
In the synchronous motor, the control means may repeatedly control the switch so as to transfer from the synchronous operation to the start operation and transfer to the synchronous operation again when power swing occurs.
In the synchronous motor, the stator core may include main core sections, from each of which a subcore section is extended in the opposite direction of the rotational direction of the permanent magnet rotor, and magnetic permeability of the main core section is greater than that of the subcore section.
In the synchronous motor, the stator may have a bobbin, which is attached to the stator core and includes a core shaft, whose axial line is perpendicular to an axial line of the permanent magnet rotor, and flanges, which are respectively provided to the both ends of the core shaft, and the A-coil and the B-coil are serially wound around the bobbin.
In the first structure, the control means controls the switching means during the start operation, and starts the motor with suppressing the input of the inverted minus side of the AC power source, which is full-wave-rectified and flows through the A-coil of the coils via the rectifying bridge circuit, so as to make the current application range of the minus side shorter than that of the plus side, then the control means turns off the switching means and turns on the switch so as to switch the connection from the start operation circuit using the A-coil to the synchronous operation circuit using the A- and the B-coils when the rotational speed of the permanent magnet rotor, which is measured by the first measuring means, reaches near the synchronous speed with respect to the power source frequency, which is measured by the second measuring means. With this action, the synchronous motor can smoothly and securely transfer from the start operation to the synchronous operation without shorting the start operation circuit.
In the second structure, the control means alternately changes the current direction of the rectified current flowing through the coils, turns on/off the third and the fourth transistors the start operation circuit so as to make the current application angular range, in which the current flows to the coils during one turn of the permanent magnet rotor, of the A-coil greater than that of the B-coil and converge the rectified current to the A-coil during the start operation, turns off the third and fourth transistors, which are connected to the B-coil, and turns on the first and second transistors, which are connected to the A-coil when the rotational speed of the permanent magnet rotor, which is measured by said first measuring means, reaches near synchronous speed with respect to the frequency of the power source, which is measured by the second measuring means, and controls the switch to change the connection from the intermediate tap to the B-coil so as to transfer the synchronous operation by the synchronous operation circuit, so that the synchronous motor can smoothly and securely transfer from the start operation to the synchronous operation without shorting the start operation circuit.
Especially, in the first and the second structures, no brushes and no commutators are provided, so sparking, which occurs when the current direction is changed during the start operation, can be prevented, so the safety and the reliability of the synchronous motor can be improved. Unlike the conventional synchronous motors, some mechanical parts, e.g., the commutator, the brushes, the switches, can be omitted, so the synchronous motor can be small in size and manufacturing cost can be reduced.
In the first and the second structures, the control means repeatedly controls the switches so as to transfer from the synchronous operation to the start operation, then transfer to the synchronous operation again when power swing occurs, so the synchronous motor can operate with high safety and reliability.
In the first and the second structures, if the stator core includes the main core sections, from each of which the subcore section is extended in the opposite direction of the rotational direction of the permanent magnet rotor, and the magnetic permeability of the main core section is greater than that of the subcore section, starting dead points of the permanent magnet rotor can be removed and stable rotation can be realized. In a two-pole and three-slot type motor, unlike the case of forming coils in a stator core, a space for accommodating the coils can be broader, so that number of turn of the coils can be increased so as to increase the power of the synchronous motor.
In the first and the second structures, if the stator has the bobbin, which is attached to the stator core and includes the core shaft, whose axial line is perpendicular to the axial line of the permanent magnet rotor, and the flanges, which are respectively provided to the both ends of the core shaft, and the coils are serially wound around the bobbin, a wasteful space, which is formed by the output shaft piercing through the stator core in the conventional motor, is not formed, so that the space for accommodating the coils can be broader, the number of turn of the coils can be increased, and the power of the synchronous motor can be increased.
In the first and the second structures, even if the power source frequency is changed, such as 50 Hz, 60 Hz, 100 Hz, the synchronous motor can be use without changing detail design, so the synchronous motor can be employed in wide fields.